Compacted heater for electronic tubes



Nov. 24, 1959 c. F. MILLER ET AL 2,913,805

' COMPACTED HEATER FOR ELECTRONIC TUBES Filed Oct. 28, 1955 INVENTORS Carl F. Miller 8 Ernest F. Smart.

ATTORNEY WITNESSES United States ,Oflce j 2,913,805 COMPACTED HEATER FOR ELECTRONIC TUBES Carl F. Miller, Bath, and Ernest F. smart Horseheads, N.Y., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October as, 1955, Serial No. 543,475

3 Claims. 01. 2945.14

This invention relates to a method and apparatus for inserting a bundle of strands of wire into a container and, more particularly, to insertion of a folded' heater into a cathode. t

The heating element for indirectly heated cathodes is often comprised of a number of straight folds of insulated coated wire bundled into 'the cathode sleeve with the two ends of the 'wire connected toan electrical heating source. The cathode sleeve usually consists of a tubular sleeve of a material such as nickel with an electron emissive coating thereon of a suitable oxide material. form of a zigzag or M-shaped fold. The heater consists of a predetermined length of a particular size wire in accordance with the ohmic value desired folded upon itself. The heater wire in specific. example may be of extremely small diameter ranging from approximately one mil to one-tenth of a mil of a material such as 'tungsten. The wire is normally covered with a relatively.

heavy baked-on coating of a suitable frangible insulated material capable of separating and insulating the several) legs or courses of the folded heater structure; This insulating coating may be. of material such as aluminum oxide applied by a drag coating process and then baked onto the wire to a thickness of about four mils.

The folded heaters are so. named because they are folded or wound on spade winding machineswhich are well known in the art. The edges of the spade cause the insulating coating to break away atthe apexes orbights of the folds, exposing a portion of bare wire. Since the tungsten wire is inherently very springy when cold worked, the heater has a tendency to unwind itself to a large degree, as illustrated in Fig. 2. In this unwound condition it is obvious that it would be very diflicult and time consuming to manually gather the bundle consisting of thelarge number of legs into proper shape for insertion into a cathode. Trays with recesses have been provided to retain the individual legs of the heater, but this has been successful only to a degree, and subsequent manual insertion results often in crossed and twisted legs and chipping of the insulating coating near the bights, resulting in shorts between legs and heater to cathode shorts and subsequent tube failures in the field.

Accordingly, it is an object of this invention to provide an improved method of insertion of the heater wires into a cathode to obtain an improved electronic tube device.

It is another object to provide an improved method of handling a folded type heater in the tube assembly process.

The folded heater element is usually in the I 2,913,805 "fPat ented Nov. 24, 1959 These and other-objects are effected by our invention, as will be apparent from the following description taken in accordance with the accompanying drawings, throughout which like reference characters indicate like parts, and in which: i p I I Figure 1 is a view "partly cut away illustrating a folded I heater within a cathode;

Fig. 2 illustrates a folded heaterwhen no restraining force is appliedto the bundle illustrating the manner in whichthe heater unwinds if not restrained;

Fig. 3 is an enlarged view of a compacted heater showing the area covered by the binder coating;

Figs. 4 to 8 are diagrammatic views illustrating several steps in the method of assembly and insertionof a folded heater into a cathode according to our invention.

'Referring in detail to Figs. 4 to 8, the method of obtaining a compact folded heater and insertion into a cathode is'illustrated. In Fig. 4, the heater 11 is wound on a mandrel 12 in the form shown or a drum-type mem ber, in a manner well known in the art. The coated heater wire is fed onto the jaws 14 of the mandrel 12 cut automatically from agspool of heater wire to the proper length and theheater connector portions 16 are cleaned.'

After theindividual heatefll is Wound and formed, a

' slightly smaller inside dimensions than those of the oath-- ode to assure that thefinalheater assembly will easily slip into-the cathode sleeve. For example, in the case of a 6CB6 type receiving tube, the slots 22 in the tray 20 have a dimension of .075 inch by .021 inch which is wellbelow the inside dimension of the 6CB6 cathode which is .096 inch by .026 inch. The. entrance sides of the slots 22 should also be provided with generous chamfer portions 24to assistlinthe insertionL- .In the case of: heaters of a shape such as provided for a circular type cathode sleeve, the openings 22 in the trays 20 shouldbe of a diameter of 10 to 20% less than the inside diam? eter of the cathode.

Referring to Figs. 5 and6, it should be noted that the heater bundle 11 is inserted with the extended connector portions 16 upward and the heater 11 pushed down .so that the ends ofthe connector portions 16 arev substantially flush-with the top surface of the magazine tray 20. In this-manner the very flexible connector portions 16 of the heater 11 are protected from any damage. In a specific embodiment shown, the trays 20 have a thickness of approximately one-half the length of the heater 11.

After the magazine tray 20 is completely loaded, the tray 20 is moved to the next position, illustrated by Fig. 6. The heaters 11 are dipped uniformly for one second or less into binder bath 26. It is only necessary that the heaters 11 be immersed approximately one to two millimeters into the solution since capillary attraction draws the binder up forming a protective coating 30, illustrated in Fig. 3, downward approximately half way on the heater bundle 11.

There are numerous organic binders suitable for practice of the invention, and it is only necessary that the binder be of a hardenable liquid and also be heat decomposable or vaporizable. A suitable binder would be a solution of heat depolymerizable resins. These resins, on heating in the range of 250 C. to 500 C. completely depolymerize or decompose into simpler components,

which are relatively volatile liquids or gases and canbe readily vaporized and recondensed, or pumped off in the case of gases. This type of coating 30 may be handled with ease and without fear of destroying the coating 30 and, thus, facilitates fabrication or assembly of the heater elements 11 into the cathode sleeves. During the normal exhaust of the tube, which necessarily requires heating to a temperature within the depolymerizing range of the resins, in order to degasify the various electronic components within the envelope, the vaporized binder will leave the vacuum system along with the other gases which are pumped out of the tube. These depolymerizable resins may, for example, comprise poly-N-butyl methacrylate (trade-name Lucite 44), polystyrene, or similar materials. These materials may decompose down into monomers, dimers, trimers, etc., when heated to a temperature, as above mentioned, ranging from 250 to 500 C.

It is necessary to utilize a solvent, such as toluene, to place one of the resins or a mixture thereof in solution. The solution may contain, for example, from to 70% resin by weight, depending on the viscosity desired. In one specific example, a 10 to 15% solution of Lucite 44 and toluene was found suitable.

The loaded magazine after immersion in the binder bath 26 is moved by automatic means to a dryer 32 and, in the specific case of Lucite #44 and toluene, was found to dry in the order of seconds in air and can substantially be decreased by using infra-red heating devices. The toluene is substantially evaporated.

After removal of the heaters 11 from the dryer 32, the heaters may be stored in the magazine 20 or moved by automatic means to the next assembly point where they are loaded into cathode sleeves 34 by automatic means. The coated end of the heater 11 is introduced into the sleeve 34 first.

In Fig. 3 there is shown an enlarged view illustrating the coating 30 on the compacted heater element 11, and, it should be noted that the legs are uniformly cemented into a firm assembly with all legs parallel and properly arranged. The protective coating 30 which is applied on the heater 11 is approximately .0002 inch to .0003 inch thick in the crevices and forms a tough film holding the individual legs or strands together. The protective coating or binder 30 also protects the insulating coating 36 nearest the apexes or bights from further chipping and makes loading by automatic means more feasible.

As previously explained, the heater 11 may be inserted into the cathode sleeve 34 from the tray 20 by automatic means and, therefore, no manual operation is requrred on the heater 11 during the entire forming, assembling and insertion process.

From the foregoing description, it is seen that We have provided an improved method of inserting the heater 11 within the cathode sleeve 34 and thereby obtained an improved indirectly heated cathode element for a. receiving tube. The binder 30 is completely removed during the exhaust of the tube.

While we have shown our invention in only one form, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various other changes and modifications without departing from the spirit and scope thereof.

' We claim as our invention:

1. In the method of assembling an insulated heater wire of the folded strand type into a sleeve-like cathode the steps comprising forming a folded type heater bundle, immersing one end of said heater bundle in a bath of hardenable heat decomposable binder while retaining the strands of said heater in a compact relation, removing said heater bundle from said bath and drying to provide a binder coating on said heater bundle firmly binding said strands in said compact relation, inserting said heater bundle into said sleeve and heating said bundle during the exhaust process to remove said binder from said heater bundle.

2. In the method of assembling an insulated coated heater wire into a folded strand type heater bundle and insertion into a sleeve-like cathode, the steps comprising forming said heater wire into a folded type heater bundle, compacting said folded heater bundle into a compact bundle, coating a portion of said bundle with a heat decomposable binder while retaining the strands of said heater bundle in a compact relation, drying said binder to provide a binder coating on said heater bundle firmly binding said strands in said compact relation, inserting said heater bundle into said cathode sleeve and decomposing said binder by heat process to remove said binder from said heater bundle.

3. In the method of preparing an insulated heater wire into a multiple strand heater element for insertion into a cathode the steps comprising forming said heater wire into a multiple strand heater bundle, compacting said multiple strand heater into a compact bundle, coating a portion of said heater bundle with a hardenable heat decomposable binder while retaining the strands of said heater in said compact relation, drying said heater bundle to provide a binder coating on said bundle firmly binding said strands in said compact relation, inserting said heater bundle to said cathode sleeve and decomposing said binder by heat process to remove substantially all of said binder material.

References Cited in the file of this patent UNITED STATES PATENTS 1,209,247 Bastian Dec. 19, 1916 1,932,077 Kimmell Oct. 24, 1933 2,436,907 Trimble Mar. 2, 1948 

